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Supplementary note for MFC Programming Module 24




What do we have in this Module?

  1. COleVariant Class

  2. COleVariant Members

  3. Construction

  4. Operations

  5. Operators

  6. Archive/Dump



COleVariant Class


class COleVariant : public tagVARIANT


A COleVariant object encapsulates the VARIANT data type. This data type is used in OLE automation. Specifically, the DISPPARAMS structure contains a pointer to an array of VARIANT structures. A DISPPARAMS structure is used to pass parameters to IDispatch::Invoke.

This class is derived from the VARIANT structure. This means you can pass a COleVariant in a parameter that calls for a VARIANT and that the data members of the VARIANT structure are accessible data members of COleVariant. The two related MFC classes COleCurrency and COleDateTime encapsulate the variant data types CURRENCY (VT_CY) and DATE (VT_DATE). The COleVariant class is used extensively in the DAO classes; see these classes for typical usage of this class, for example CDaoQueryDef and CDaoRecordset. The afxdisp.h must be included in order to use this class.


COleVariant Members





Constructs a COleVariant object.


Table 1.





Attaches a VARIANT to a COleVariant.


Changes the variant type of this COleVariant object.


Clears this COleVariant object.


Detaches a VARIANT from a COleVariant and returns the VARIANT.


Retrieves a byte array from an existing variant array.


Sets the string to a particular type, typically ANSI.


Table 2.




operator =

Copies a COleVariant value.

operator ==

Compares two COleVariant values.


Converts a COleVariant value into an LPCVARIANT.

operator LPVARIANT

Converts a COleVariant object into an LPVARIANT.


Table 3.




operator <<

Outputs a COleVariant value to CArchive or CDumpContext.

operator >>

Inputs a COleVariant object from CArchive.


Table 4.



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